This invention relates to an optical data storage medium and a method of producing the same. More particularly, the present invention relates to an optical data storage medium, preferably in the form of a disk or in tape format, suitable for use with optical recording and playback apparatus, which optical data storage medium comprises a textured surfaced information layer comprised of at least one encapsulated dye.
Various optical recording media and methods for recording information thereon are known in the prior art. For example, the recording of information in the form of deformations or ripples in a thermoplastic film is known, with techniques for achieving such deformations involving the steps of (1) forming a charge pattern on the surface of the thermoplastic film in accordance with the information to be recorded, (2) heating the thermoplastic to its melting point so as to permit the electrostatic forces produced by the charges to form a deformation pattern in the thermoplastic film corresponding to the charge pattern and thus to the information to be recorded, and (3) then cooling the thermoplastic film below its melting point to fix the thus formed deformation pattern in the film. Reading of the plastic film may be accomplished using well-known optical techniques. See, e.g., U.S. Pat. No. 3,952,146.
Optical recording methods in which light from a laser or other suitable light source is focused upon the surface of a recording medium with sufficient intensity to cause the formation of deformations in the surface material have also been proposed. In such methods, an information representative pattern of deformations, e.g., pits, is formed in the surface of the recording medium by suitably controlling the intensity of the focused light in accordance with the information to be recorded while relative motion is established between the recording medium and the focused light spot.
In recent years, attention has been increasingly paid to the information recording method in which information is written in a thin film of metal or the like formed on a substrate by using a laser ray or beam. According to such a method, the recording of information has been accomplished by forming holes or recesses in the metallic thin film under the action of a thermal energy beam such as a laser beam. See, e.g., U.S. Pat. No. 4,238,803.
Attention has also been paid to the use of dye layers, polymer layers, or dye/polymer layers as recording layers for optical information media. For example, Spong, U.S. Pat. No. 4,097,895, describes a recording medium which comprises a light reflecting material, such as aluminum or gold, coated with a light absorbing layer, such as fluorescein, which is operative with an argon laser light source. The thickness of the light absorbing layer is chosen so that the structure has minimum reflectivity. An incident light beam then ablates, vaporizes or melts the light absorbing layer, leaving a hole and exposing the light reflecting layer. After recording at the wavelength of the recording light, maximum contrast between the minimum reflectance of the light absorbing layer and the reflectance of the light reflecting layer exists. In this regard, note also U.S. Pat. No. 4,219,826.
Carlson, in U.S. Pat. No. 3,475,760, discloses a system for directly recording information in a thermoplastic film as a deformation by using a high energy laser scanning beam of small diameter.
Slaten, U.S. Pat. No, 4,310,919, discloses a video disk comprising an information storage layer. The information storage layer is comprised of a plastic such as polymethylmethacrylate, or blends thereof, with other resins. Included among the suitable resins for blending and use in the information storage layer are polyvinyl chloride, polyvinylidine fluoride and styrene copolymers such as styrene acrylonitrile.
Kido et al, U.S. Pat. No, 4,032,691, discloses a recording material which comprises a support and a heat sensitive recording layer thereon, which heat sensitive layer is thermally deformed, foams, colors, discolors, sublimes, evaporates or becomes transparent, translucent or opaque when exposed to radiation. The heat sensitive recording layer may comprise a metal, dye or synthetic.
Kido et al, U.S. Pat. No. 4,415,650, discloses optical recording media wherein the recording layer comprises a polymer, a dye, or a combination of both. The recording layer may be coated on a metallic layer supported by a substrate. Polymers usable for the recording layer include thioureas, thiocarbazides, thiocarbanic acid, trizoles and tetrazoles, and polyamides.
Lewis, U.S. Pat. No. 4,296,158, discloses information carrying media comprised of a substrate having an information bearing layer derived from 15 to 100% by weight of at least one polyacryloyl-containing heterocyclic monomer. Besides the heterocyclic monomer, the information layer can contain up to 85% of an ethylenically unsaturated monomer such as acrylonitrile. The information is encoded on the information carrying layer as depressions, protuberances and/or grooves. The information layer is then exposed to ultraviolet radiation in order to photopolymerize the monomers and harden the layer. The use of polyacrylonitrile in a layer into which information is to be recorded, however, is not disclosed.
Further, there is a recognition in the art of the use of surface structure to increase the contrast between recorded data and the surrounding disc surface.
For example, Craighead et al, U.S. Pat. No. 4,422,159, discloses the use of a disc which contains preformed column structures to obtain extremely high contrast. Information is written onto the disc by ablating the material from the uppermost surface of the column revealing a reflective medium below. Before treatment the material appeared black when viewed through the microscope and for each pulse a reflective region was produced.
U.S. Pat. No. 4,084,185, issued to de Lang et al, discloses an optical disc which utilizes diffraction gratings as the source of information, as opposed to a laser ablated "pit." The disc contains alternating concentric tracts of gratings which are angled to diffract light in different directions. This effectively doubles the amount of storage capacity because the two tracks adjacent to the track being read will diffract light away from the detector. In this manner a data track can act as a space or "land" allowing for an "optimum discrimination between the radiation originating from the various types of gratings." The surface diffraction of the disc is not, however, a construction part of the disc which is later ablated to reveal a bright, reflective pit. Instead, it is a structure that is added to the disc simultaneously with the addition of information.
In all of the foregoing techniques, there is involved the formation of a data storage medium and a distinct step for forming the surface irregularities.
Despite all of the techniques used in the optical recording of information and the various materials used in the construction of the information layer of such media, the search for new materials which are useful in the information layer and which provide excellent contrast and sensitivity, and the ability to record a much higher density of information, is continually on-going.
Accordingly, it is a major objective of the present invention to provide a novel optical data storage medium which is stable and on which information can be readily and effectively recorded.
It is further an object of the present invention to provide an optical data storage medium capable of extremely high density data storage.
It is another object of the present invention to provide a recording medium which comprises an information layer which is highly textured.
It is still another object of the present invention to provide a recording medium which comprises an information layer which is highly textured and comprised of at least one microencapsulated dye.
It is still another object of the present invention to provide a recording medium which comprises an information layer which is highly textured and comprised of at least one encapsulated dye.
Yet another object of the subject invention is to provide a novel method for the production of an optical data storage medium as described above which does not require an additional step for the formation of a textured surface.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and the appended claims.